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Virialization of the inner CGM in the FIRE simulations and implications for galaxy disks, star formation, and feedback

Authors
  • Stern, J
  • Faucher-Giguère, CA
  • Fielding, D
  • Quataert, E
  • Hafen, Z
  • Gurvich, AB
  • Ma, X
  • Byrne, L
  • El-Badry, K
  • Anglés-Alcázar, D
  • Chan, TK
  • Feldmann, R
  • Kereš, D
  • Wetzel, A
  • Murray, N
  • Hopkins, PF
Publication Date
Apr 20, 2021
Source
eScholarship - University of California
Keywords
License
Unknown
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Abstract

We use the FIRE-2 cosmological simulations to study the formation of a quasi-static, virial-temperature gas phase in the circumgalactic medium (CGM) at redshifts 0 < z < 5 and how the formation of this virialized phase affects the evolution of galactic disks. We demonstrate that when the halo mass crosses ∼1012 Me, the cooling time of shocked gas in the inner CGM (∼0.1Rvir, where Rvir is the virial radius) exceeds the local free-fall time. The inner CGM then experiences a transition from on average subvirial temperatures (T = Tvir), large pressure fluctuations, and supersonic inflow/outflow velocities to virial temperatures (T ∼ Tvir), uniform pressures, and subsonic velocities. This transition occurs when the outer CGM (∼0.5Rvir) is already subsonic and has a temperature ∼Tvir, indicating that the longer cooling times at large radii allow the outer CGM to virialize at lower halo masses than the inner CGM. This outside-in CGM virialization scenario is in contrast with inside-out scenarios commonly envisioned based on more idealized simulations. We demonstrate that inner CGM virialization coincides with abrupt changes in the central galaxy and its stellar feedback: the galaxy settles into a stable rotating disk, star formation transitions from “bursty” to “steady,” and stellar-driven galaxy-scale outflows are suppressed. Our results thus suggest that CGM virialization is initially associated with the formation of rotation-dominated thin galactic disks, rather than with the quenching of star formation as often assumed.

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